1. Technical Field
The present invention relates to a sheet detecting device for detecting whether sheets are conveyed and for detecting whether a double feed of the sheets is occurred. The present invention also relates a double feed determining device using the sheet detecting device, and an image reading apparatus.
2. Back Ground
In a related art, a sheet detecting device, which uses ultrasound to determine whether sheets are conveyed and a double feed of the sheets occurred, is proposed. JP-A-2004-175570 discloses a sheet detecting device including a plurality of ultrasound transmitters, a signal transmitter, a plurality of ultrasound receivers and a signal receiver. The signal transmitter transmits the ultrasound to the plurality of ultrasound transmitter. Each of the plurality of ultrasound transmitters transmits the ultrasound toward a conveyed sheet. The plurality of ultrasound transmitters are arranged parallel in a direction perpendicular to a conveying direction of the conveyed sheet. The plurality of ultrasound transmitters are provided to face to each of the plurality of ultrasound transmitters in a direction vertical to a plane of the conveyed sheet, with interposing the sheets. Each of the plurality of ultrasound receivers receives the ultrasound, which reach through the conveyed sheet after transmitted from the plurality of ultrasound transmitters. In this manner, the apparatus disclosed in JP-A-2004-175570 detects the conveyed sheet using the plurality of ultrasound transmitters and the plurality of ultrasonic receivers and determines whether the sheets are conveyed, that is, whether the double feed of sheets occurred, when various sized sheets are conveyed.